Conventionally, as one example of a heating device that is provided with multiple control loops, there have been the oxidizing/diffusing furnaces as illustrated in FIG. 5. Silicon wafers 105 are loaded into the inside of a quartz tube 104 within an oxidizing/diffusing furnace 100. Temperature sensors 102-1 through 102-3 measure the temperatures PV at control zones Z1 through Z3 that are heated by respective heaters 103-1 through 103-3. Regulators 101-1 through 101-3 calculate operating quantities MV that will cause the respective temperatures PV, measured by the temperature sensors 102-1 through 102-3, to go to the temperature set points SP, and output these operating quantities MV to the heaters 103-1 through 103-3. In this way, the oxygen and the silicon wafers 105 that have been introduced into the quartz tube 104 of the oxidizing/diffusing furnace 100 are heated to form an oxide layer on the surfaces of the silicon wafers 105. In the heating device illustrated in FIG. 5, the individual regulators 101-1 through 101-3 form three individual control loops for controlling respective temperatures PV of the control zones Z1 through Z3.
In the heating devices that are provided with multiple control loops, overshooting occurs in the control loop wherein the temperature ramps up first, due to the temperature interferences between the control loops when the temperatures ramp-up in each of the control zones simultaneously, requiring extended time until a stabilized state of control is achieved, thus causing a loss in the equipment operating efficiency.
Given this, there has been a proposal for a method for controlling the operation by ramping up the set points SP (that is, an operation wherein the set points SP are increased gradually while sequentially measuring the state of control (See Japanese Patent 3798607 (“JP '607”)). In the controlling method disclosed in JP '607, the degree of progress in the step response of the first control loop, wherein the temperature ramp-up is the slowest, is calculated, and the temperatures in the other control loops, excluding the first control loop, are modified automatically to synchronize with the temperature of the first control loop, to correct the set points SP of the other control loops based on the degree of progress in the step response.
When implementing this type of controlling method, ordinary regulators, or the like, that are equipped in heating devices are usually used as-is as PID control calculating devices for calculating the operating quantities MV for the individual control loops, and usually a higher-level controller, other than the regulator, is used as SP calculating means for correcting the set points SP. Consequently, it is necessary to send the controlled quantity PV to the SP calculating means from the individual PID control calculating means continuously during the temperature ramp-up process, and necessary to send the set points SP to PID control calculating means from the SP calculating means.
In the case of the controlling method disclosed in JP '607, there is a problem in that when an error occurs in the signal transmitting function between the PID control calculating means (for example, the regulator) and the SP calculating means (for example, the higher-level controller) during the temperature ramp-up process, it is necessary to shut down the temperature ramp-up itself, which, in any event, makes it impossible to perform the planned control operation.
Note that the problem point as described above is not limited to temperature ramp-up control, but occurs similarly in, for example, temperature ramp-down control, and in pressure control.
The examples of the present invention solve problems such as set forth above, and the object thereof is to provide a controlling method and device wherein, when a set point has been changed, it is possible to perform control wherein the frequency of signal transmission between the control calculating means and other means is reduced and wherein the times at which the set points, after the controlled quantities have been changed in the individual control loops, are reached are essentially simultaneous.